Invasion... Level 1: Contamination

Invasion... Level 1: Contamination is a single-level PWAD for Doom that was released in 1994. It was designed by Andy Chen and Claude Martins. It was followed by Invasion... Level 2: The Upper Decks.

Secrets

 * 1) Go through the first door and turn right.  Near the first armor bonus you reach are two alcoves.  Pressing the western one opens up a secret door opposite leading to a passage with a shotgun guy and two health bonuses (on medium and hard skills only), and a megaarmor which lies on a teleporter to the south-east area.  Both the passage to the teleporter and the teleporter itself count as secrets. (sector 27)
 * 2) See #1.  It is not possible to receive credit for this secret as the player teleports before stepping on the sector. (sector 28)
 * 3) From the blue key, head east then south.  Continue through a fake wall, at the end of which is a soul sphere. (sector 118)
 * 4) Heading north from the blue key area, there are two passages to the west.  Between them is a fake wall, through which is a partial invisibility and a lift leading up to a berserk. (sector 122)
 * 5) The room with the teleporters leading to the red key area has a secret door on its north wall leading via a second door and a lift to the yellow key and a box of shells.  Both the sector between the doors and the yellow key sector count as secrets. (sector 256)
 * 6) See #5. (sector 179)
 * 7) Head north from the blue key area then turn right at the end and right at the end of that path.  Immediately on the left is a fake wall through which is a shotgun guy on a platform (on medium and hard skills) and a nukage pit down below, which contains a chainsaw as well as (on medium and hard skills) a medikit and a spectre (two on hard skill).  There is a switch which causes the platform to lower, allowing you to jump across and out of this area.  Note that entering this area activates a crushing ceiling. (sector 285)

Bugs
Because one secret cannot be achieved (see Secrets section), the maximum secrets percentage obtainable is 85%.

If the player goes through the teleporter in Secret #2, he will be stuck in the south-east area unless he both has the red key and has pressed the switch near the computer map.

Current records
The records for the map at the Doomed Speed Demos Archive are:

Things
This level contains the following numbers of things per skill level: